Adduct "speculation" in LC/MS

[vlaselaurian]

Hi all,
It is well known that some compounds tend to form adducts, even in presence of low concentration of ions (eg Na).
In this case, there is a good solution to "help" in formation of these adducts, adding the ion in mobile phase (e.g. 1 mM sodium acetate) ??
I found an application using this technique at: https://www.chem.agilent.com/scripts/li ... WHID=16640
What is the effect of 1 mM of non-volatile Na acetate on MS??
But about using Ag salts or other for the same purpose?

Any opinion is wellcome.
Thank you,
laurian vlase

[MG]

You can use sodium acetate to shift everything to sodium adducts, but 1mM is probably too much. Think micromolar. According to

RCMS, 11 (1997), 1083-1088

0.3 mM was ideal for analysis of an ester compound being analyzed, as far as shifting everything over to M+Na. Notice however that the authors already had plenty of M+Na without adding sodium, so for the purposes of SIM or MRM quantitation they were reducing their signal (and probably S/N as well). However the advantage of adding sodium was in greater linear dynamic range.

I am working on a project right now, looking at neutral compounds in ESI(+). Without addition of sodium, they form a mixture of sodium and ammonium adducts. I found that 0.3 mM was effective but suppressed the signal a great deal. 0.03 mM was also effective but with less signal suppression.

[vlaselaurian]

Thank you for answer.
Does anybody seen adducts with other metals, like Ag+, Mg2+ and so on?
Regards.

[MG]

I have not, but I imagine it is possible if salts of these metals were added to the mobile phase (or added to sample in the case of direct infusion). Keep in mind that Ag would split your signal due to the isotope distribution. And Mg2+ would give doubly-charged ions.

[Kostas Petritis]

Vsaselaurian,

The concept of using metals for enhancing the response of non-polar and/or difficult to ionise compounds (like phenolic ones) has been previously investigated so you should be able to find several articles on this.

If I remember well it was introduced in ASMS sometime on the year 2000 or so. Also I think that Ag+ was one of the most succesful metals used, I guess due to its complexation abilities. If you do not introduce these metals somehow (i.e. post-column with a Tee) then you will propably won't see their adducts as they are not as abundant as Na+.

[vlaselaurian]

Regarding AgNO3 post column adding,
1. what is the proper concentration to be used? (conc. in final flow)
2. there is the possibility that Ag+ to be reduced to Ag and deposit on the source / capillary and contaminate the system?
thank you.